Terrorist use of radioactive nuclear materials is a serious threat for mass destruction or disruption of civil and military activities. Most worrisome is the use of nuclear devices that may cause massive casualties to people and damage to structures. A device that combines radioactive materials with conventional explosives to make a radiological dispersion device is commonly called a “dirty bomb.” The procurement of nuclear materials for this purpose, the construction of the bomb, and its use are all easier than those of a nuclear weapon. Thus, it is important to detect the transport of the radiological dispersion devices and the materials needed for their construction. These materials emit gamma rays or neutrons, which can be detected to show the presence and amounts of such materials using radiation detectors.
High-efficiency gamma-ray and neutron detectors are required to provide information to intercept nuclear materials and devices prior to an attack, as well as for radiation assessment and attribution after an attack. Desirable properties of radiation detectors are:                High detection efficiency over a wide energy range        High optical (and electrical) gain in the specified range        Low background noise        Large dynamic range (speed) and linearity        Low operating bias voltages        Robust design for a wide operating temperature range.        
Some other usages of the detectors are for jet and rocket engine flame detection, medical imaging, astronomy, and oil drilling.
The three commonly-used classes of detectors for Ultra Violet (UV), deep UV, X-rays and gamma rays are: (a) scintillation crystals coupled to photodetectors or photomultiplier (PM) tubes (as shown in FIG. 1), (b) high pressure ionizing gas-based detectors, and (c) semiconductor detectors.
The most common scintillation detector is NaI(Tl), usually coupled to a PM tube. NaI detectors have relatively poor energy resolutions. This limits their use in high background situations, or for unknown sources with many closely-spaced peaks. Gamma-ray peaks from a weak source will be difficult to observe in a relatively high background environment, and peaks that differ by a few percent in energy will usually be unresolved. Similarly, Gas-based detectors have poor resolution, and are bulky with poor vibration performance.
An excellent solution for Gamma ray detectors is to couple modem Ce-based scintillator crystals with room/high temperature semiconductor photodetectors, which can replace the function of the PM tube. Modem LaBr3 and CeBr3 scintillators emit radiation in the 320-440 nm range, as shown in FIG. 2. These crystals offer excellent decay lifetimes and reasonable detector lengths, as well as excellent light output (>68000 Photon/MeV), as shown in FIG. 3.
Semiconductor radiation detectors have unique capabilities and provide superior performance in many respects over other kinds of detectors. The energy resolution achieved with semiconductor-based detectors is superior to that of other technologies. The faster charge-collection times of solid-state detectors provide them with the ability to process higher counting rates. Their compactness allows the measurement of intensity variations over small distances. Furthermore, the semiconductor detectors can be efficient, compact, and rugged.
Germanium (Ge) semiconductor diodes are the gold standard for the gamma-ray detectors, with resolutions of typically 1.3 keV (0.2%) at 662 keV. This allows precise determination of peak energies, separation of close-lying peaks, and detection of weak peaks in the presence of a strong background. Ge detectors have the disadvantage that they must be operated at low temperatures (less than 100 K) to avoid electronic noise, which is an obvious and severe logistical problem. Some of the prior art references/research groups related to this technology are listed here:                U.S. Pat. No. 5,394,005, Brown et al., describing SiC photodiode, from GE        U.S. Pat. No. 5,589,682, Brown et al., describing photocurrent detector, from GE        U.S. Pat. No. 6,573,128, Singh, describing SiC Schottky devices, from Cree        U.S. Pat. No. 6,838,741, Sandvik et al., describing avalanche photodiode, from GE        U.S. Pat. No. 7,026,669, Singh, describing lateral channel transistor        U.S. Pat. No. 6,849,866, Taylor, describing optoelectronic devices, from U. of Connecticut        U.S. Pat. No. 6,455,872, William et al., describing photodetector, from Hitachi        U.S. Pat. No. 5,384,469, Choi, describing voltage tunable multicolor infrared detectors, from US Army        U.S. Pat. No. 4,833,512, Thompson, describing heterojunction photodetector with transparent gate, from ITT        U.S. Pat. No. 4,353,081, Allyn et al., describing graded bandgap rectifying semiconductor devices, from Bell Labs        U.S. Pat. No. 6,965,123, Forbes et al., describing SiC devices, from Micron Tech.        U.S. Pat. No. 6,137,123, Yang et al., describing GaN heterojunction phototransistor, from Honeywell        U.S. Pat. No. 5,311,047, Chang, describing amorphous Si/SiC heterojunction color-sensitive phototransistor, from Taiwan, National Science Council        Hans Rabus, from Physikalisch-Technische Bundesanstalt        Peter Sandvik and Emad Andarawis, from GE Global Research        